#include <iostream>
#include <cmath>
#include <string>
using namespace std;
int main() {
    string s;
    int l;
    cin >> s;
    l = s.length();
    if (s.substr(0, l/2) == s.substr(ceil(l / 2), -1)) {cout << "YES" << endl;}
    else {cout << "NO" << endl;}
    return 0;
}